Stroke is the third leading cause of death worldwide and can be defined as the rapidly developing loss of brain function(s) due to interruption in the blood supply to the brain. According to the World Health Organisation, 15 million people per year suffer stroke worldwide, with 5 million dying and a further 5 million being permanently disabled. High blood pressure is estimated to be a contributing factor in 12.7 million of these 15 million stroke cases. In the UK, approximately 150,000 people have a stroke each year and stroke accounts for around 53,000 deaths per year. Stroke costs the economy an estimated £8 billion per year in England alone and stroke patients occupy approximately 20 percent of all acute hospital beds and 25 percent of long term beds.
Stroke can be classified into three sub-types:                i) Ischaemic stroke (IS) occurs when blood supply to the brain is decreased, resulting in brain damage. An ischemic stroke occurs when a blood vessel becomes blocked, usually via a blood clot. This clot may form locally at an atherosclerotic plaque (thrombotic stroke) or alternatively may occur due to a travelling particle or debris that has originated from elsewhere in the bloodstream (embolic stroke);        ii) Transient ischaemic attack (TIA) is a ‘mini stroke’ that occurs when blood supply to the brain is temporarily decreased. A TIA is diagnosed if symptoms are quickly resolved (within 24 hours with the individual returning to normal health); and        iii) Haemorrhagic stroke (HS) occurs when blood accumulates within the skull vault, usually when a weakened blood vessel ruptures. Haemorrhagic stroke can be classified into two major subtypes, namely intracerebral (within the brain tissue) and subarachnoid (around the surface of the brain and under its protective layer).        
IS and TIA account for approximately 85% of all stroke cases and HS accounts for 15%. In order to minimise neurological damage following stroke it is crucial that stroke patients are rapidly and accurately diagnosed, so that appropriate treatment can be administered. For example, in order to break down clots thrombolytic therapy such as tissue plasminogen activator (TPA) can be administered. However, such therapy is only warranted in IS and is detrimental in HS. The nature of TIA does not require such therapy and blood thinners such as warfarin and aspirin are prescribed in such cases.
At present, if stroke is suspected, physical symptoms are evaluated and a computerised tomography (CT) scan is usually performed. A CT scan has good sensitivity for identifying HS patients (approximately 90% sensitivity) but poor sensitivity for identifying IS and TIA patients (approximately 20% sensitivity). In practice minimal or no tissue damage occurs for TIA due to its transient nature, therefore CT scanning is ineffective as a diagnostic technique. Magnetic Resonance Imaging (MRI) has improved sensitivity for IS diagnosis (up to approximately 80%) but increased time requirements, machine accessibility, and high cost have limited its use for stroke diagnosis. The poor sensitivity of CT scanning for the detection of IS and TIA means that a biological fluid-based diagnostic biomarker tests for detecting IS and TIA would be an invaluable tool to aid clinicians in the diagnosis of stroke sub-type. Biological fluid-based biomarkers have the potential to expedite and increase the accuracy of stroke diagnosis.
Various candidate biomarkers have been proposed for the diagnosis of stroke and stroke sub-type delineation and there are several descriptions of IS/TIA versus HS discrimination in the prior art, for example EP1238284, WO 2010/086697, WO 2010/012834, and WO 2002/012892.
EP1419388 discloses data that distinguishes IS from HS and all stroke types from non-stroke controls. However, none have thus far found use in clinical practice and there is a real clinical need for biomarkers of all three stroke sub-types that have high sensitivity and specificity to enable accurate diagnosis.
Differential diagnosis between the three different stroke sub-types using a blood test would facilitate a more informed clinical decision, potentially render unnecessary expensive and less expeditious neuroimaging diagnostics, and could improve the clinical outcome for patients.